These studies were undertaken to investigate the effects of selected environmental chemicals on the immune competence of laboratory animals. The topics of present interest include effects of transplacental exposure and effects of of neonatal exposure. Chemicals investigated to date are 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), other dioxins (OCDD, HpCDD, and HxCDD, methyl mercury, lead, diethylstilbesterol (DES), and methyl butyl ketone (MBK). Results of studies completed to date show: TCDD to cause similar immunosuppression in Fischer X Wistar F animals as previously seen in Fischer rats (suppression of cell mediated immune function); other dioxins to have no effect on parameters of immune function in cattle exposed in utero and during nursing through mothers exposed to dioxin contaminated pentachlorophenol treated wood; lead to suppress both cell mediated and humoral immune functions; and DES to cause humoral immune enhancement in male offspring of treated female mice.